Usher Syndrome is a hereditary disorder that causes hearing loss (HL) and retinitis pigmentosa (RP). The three major clinical types, Usher syndrome types I, II and II, are distinguished by severity of hearing loss and by presence or absence of vestibular dysfunction. Type I patients have severe hearing loss, RP, and vestibular dysfunction. Type I patients have severe hearing loss, RP, and vestibular dysfunction. Type III is distinguishable from types I and II by a progressive HL and variable vestibular deficit. At least ten distinct genetic loci are now believed to be associated with the three clinical types of Usher syndrome. We have collected the world's largest series of Usher families, a unique resource suitable for the studies proposed in this project. We propose to work towards a clarification of the problem of heterogeneity by testing hypotheses relating to the existence of all Usher loci and by estimating the relative contribution of each to the overall frequency of Usher syndrome. In addition, we propose to determine the distribution of mutations in MYO7A and USH2A, to identify and characterize the genes causing Usher types IIb, Ia, Id/f, Ie, and III, and to localize the gene for Usher type II c and any other new Usher genes uncovered by this research. Since Usher Syndrome results in the loss of the two most vital human senses, the burden to patients with this disorder is tremendous. It acts to isolate them from the rest of society and reduces their ability to act independently. Close to 1 in 15,000 individuals are affected with Usher Syndrome. The capability of Usher subtype diagnosis disorder will be enhanced leading to more accurate genetic counseling. A better understanding of the underlying etiology of Usher Syndrome is a critical first step towards the development of effective therapy. Usher syndrome offers a way of studying how the two major senses are related and answers to questions regarding the etiology of Usher Syndrome will reveal important and novel information about the developmental, metabolic and/or regulatory pathways common to normal retinal and auditory function.